Disjoint hypercyclicity, Sidon sets and weakly mixing operators

Abstract: We prove that a finite set of natural numbers $J$ satisfies that $J\cup{0}$ is not Sidon if and only if for any operator $T$, the disjoint hypercyclicity of ${T^j:j\in J}$ implies that $T$ is weakly mixing. As an application we show the existence of a non weakly mixing operator $T$ such that $T\oplus T^2\ldots \oplus T^n$ is hypercyclic for every $n$.